Many luminous devices based upon the use of controlled, glowing electrical discharges through inert gasses, especially neon, are known. Most display devices based upon this concept utilize a tortuous path defined by a multiply bent transparent or translucent vitreous tube having electrodes at its terminations. Other methods of producing display devices without using bent vitreous tubes have also been proposed. U.S. Pat. No. 1,949,963 describes the use of multiple flat plates assembled so as to produce a continuous, tortuous, interior channel. The discharge path assembly consists of five flat plates of transparent, insulating material. The two outside plates are solid while the middle inside plate is perforated in such a manner that the engraved channels in the remaining two plates can form a continuous path that crosses back upon itself by means of the perforations. U.S. Pat. No. 1,825,399 features the use of only two glass plates together with the use of either tubular holes cut into one of the plates or engraved passages, which are angled with respect to the glass plate surface, crossing over each other and thereby permitting the formation of a continuous, tortuous pathway which, in its two dimensional projection, crosses over itself.
The use of opaque or translucent letters or symbols applied by painting or by other means has been described in several patents. U.S. Pat. No. 1,724,584 provides for the incorporation of external letters on neon or other gas filled discharge tubes by painting or other means. U.S. Pat. No. 1,805,798 refers to the use of a mirror in combination with an electric sign. A silvered piece of glass in which a portion of the silvered side has been removed is fabricated in such a fashion that the letters or symbols comprising the sign are legible from the glossy side of the silvered glass. Illumination of the letters or symbols is provided by a light bulb placed behind the mirrored glass.
None of these display devices allow the preparation of a luminous gas-discharge display device formed by cutting channels into only a single plate of vitreous insulating material. Furthermore, all of the glow discharge channels that define the desired letters or symbols in these devices are of constant cross-sectional dimension in the defining region. The following drawings illustrate how the objects of the present invention are accomplished.